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During her regular walk to the research facility, scientist the researcher stoops near a shallow pond surrounded by thick plants and retrieves a compact plastic sound device.

The device was left there overnight to record the characteristic croaks of the Scinax quinquefasciatus, recognized by local scientists as an non-native threat with effects that scientists are just beginning to comprehend.

Despite teeming with remarkable animals – such as ancient giant tortoises, marine lizards, and the famous birds that sparked Charles Darwin's evolutionary theory – the Galápagos archipelago off the coast of Ecuador had historically been devoid of frogs and toads.

In the late 1990s, this changed. Some small amphibians made their way from continental the mainland to the archipelago, likely as stowaways on cargo ships.

DNA studies indicate that, through time, there have been repeated accidental arrivals to the islands, and the amphibians now have a firm presence on several islands: multiple locations.

The population is growing so rapidly that researchers have been finding it difficult to keep track, calculating numbers in the millions on each island, across urban and agricultural areas, but also in the conservation Galápagos national park.

When the biologist tagged amphibians and attempted to find them in the following week and a half, she could find just one tagged frog occasionally, suggesting their populations were massive.

They estimated 6,000 frogs in a solitary pond. "Our estimates are still very conservative," states the researcher. "I am quite certain there are additional numbers."

Deafening Noise and Growing Concerns

The amphibians' abundance is clear from the acoustic chaos they cause. "The number of frogs and the noise – it's really incredible," says the scientist.

For the researchers, their nocturnal mating calls are helpful in determining their existence in remote areas, using audio devices like the one near San José's workplace.

But local farmers say the calls are so loud they keep them up at night.

"During the wet season, I constantly hear their croaks and they're really loud," says a local coffee farmer from the island.

"Initially it was a surprise, observing the initial frogs in the area," says the farmer, who started observing their abundance about three years ago when one jumped on her hand as she was stepping out of her house.

Ecological Impact Stays Unknown

The noise isn't the fundamental problem, though. While the species has been in the islands for nearly 30 years, scientists still know very little about its effect on the islands' precariously balanced land and water environments.

On islands, it is very typical for non-native species to thrive, as they have few of their enemies. The Galápagos counts 1,645 invasive types, many of which are significantly affecting the survival of its native ones.

A 2020 research suggests the non-native frogs are voracious bug eaters, and might be disproportionately consuming rare bugs found only on the archipelago, or reducing the food sources of the region's uncommon avian species, disrupting the ecosystem balance.

Unusual Traits and Control Challenges

The island amphibians have exhibited some unusual characteristics, including living in slightly salty water, which is uncommon for frogs.

Their development process is also extremely inconsistent, with some tadpoles becoming frogs very rapidly and others taking a extended period: the researcher witnessed one which remained as a larva in her lab for six months.

"We truly don't know this aspect," she says, concerned the tadpoles could be impacting the islands' freshwater, a very limited resource in Galápagos.

Techniques to control the frogs in the early 2000s were largely ineffective. Conservation officers tried capturing significant quantities by hand and gradually raising the salinity of ponds in vain.

Studies suggests spraying coffee – which is highly poisonous to frogs – or using electrical methods could assist, but these approaches aren't necessarily secure for other rare Galápagos organisms.

Without solutions to more of the basic issues about their biology and effect, removing the amphibians might not even be the correct way to advance, says San José.

Funding Challenges for Research

While she expects the growing use of eDNA methods and DNA analysis will help her group understand of the invader, funding for the research has been hard to obtain.

"Everybody wants to give support for preserving frogs," says San José. "But it's harder to find funding for an invasive frog that you might want to control."